How long is Neptune's orbit?

Neptune takes 164.8 years to go once round the Sun. It is travelling at 5.47 km/s at the moment — a speed that changes through the orbit, fastest at perihelion and slowest at aphelion.

What shape is Neptune's orbit?

An ellipse with the Sun at one focus, not at the centre. Its eccentricity is 0.0089, derived here from the perihelion and aphelion distances rather than quoted: 29.81 AU at closest and 30.34 AU at furthest, a difference of 79,759,180 km.

Where is Neptune in its orbit now?

29.88 AU from the Sun — 4.47 billion km — which is 13% of the way from its closest point to its furthest. It next reaches perihelion on 11 September 2042.

Neptune

Neptune's orbit

Once round the Sun every 164.8 years, on an ellipse drawn here from the ephemeris rather than from a formula.

Looking down on the plane of the ecliptic, traced from the ephemeris over one full orbit of 165 years. Uranus’s orbit is the faint one, for scale. The Sun sits off the centre of the ellipse — that offset is the eccentricity, and it is why the two distances differ.

Orbital period: 164.80; years for one lap
Eccentricity: 0.0089; 0 would be a circle
Semi-major axis: 30.07; AU · the orbit's average radius
Speed now: 5.47; km/s, from the ephemeris

What is worth knowing about it

Neptune was found by mathematics before it was seen: irregularities in Uranus's orbit pointed to where it had to be, and it was spotted within a degree of the prediction. It has completed just one orbit since that discovery in 1846.

The shape of it

Neptune does not travel a circle. It comes as close as 29.81 AU (4.46 billion km) and goes as far as 30.34 AU (4.54 billion km) — aphelion is 1.02 times further out than perihelion, a swing of 79,759,180 km. At 0.0089 its orbit is very nearly a circle — draw it to scale and the difference from one would be thinner than the line.

Because the Sun sits at a focus rather than the centre, Neptune does not move at a constant speed either. It runs fastest when it is closest and slowest when it is furthest, sweeping equal areas in equal times — which is Kepler's second law, and is visible in the diagram above as the uneven spacing of a constant time step.

Where it is now

Today Neptune is 29.88 AU from the Sun, 13% of the way from perihelion to aphelion, travelling at 5.47 km/s. It reaches perihelion on 11 September 2042 at 29.81 AU.

Common questions

How long is Neptune's orbit?: Neptune takes 164.8 years to go once round the Sun. It is travelling at 5.47 km/s at the moment — a speed that changes through the orbit, fastest at perihelion and slowest at aphelion.
What shape is Neptune's orbit?: An ellipse with the Sun at one focus, not at the centre. Its eccentricity is 0.0089, derived here from the perihelion and aphelion distances rather than quoted: 29.81 AU at closest and 30.34 AU at furthest, a difference of 79,759,180 km.
Where is Neptune in its orbit now?: 29.88 AU from the Sun — 4.47 billion km — which is 13% of the way from its closest point to its furthest. It next reaches perihelion on 11 September 2042.

Positions from VSOP87 via Astronomy Engine, accurate to within one arcminute. The orbit above is traced by sampling a full period rather than drawn from elements, so the tilt and the off-centre Sun are the real ones. See Neptune’s distance from the Sun, Neptune right now, or watch the whole system move in the live simulation.